The present invention relates to the manufacture of joint prosthesis, and particularly a femoral prosthesis for a hip joint.
The femoral prosthesis for a prosthetic hip joint includes an elongated stem that is embedded within the medullary canal of the femur. The elongated stem body transitions at a transition region that terminates along the stem axis in a driver platform that provides a surface for driving the stem into the medullary canal. The transition region merges into a shoulder (which forms part of the driver platform) that is at an angle relative to the centerline of the stem that bears against a prepared surface of the femur. A neck and collar project from the shoulder, each configured to engage a ball joint component that forms part of the prosthetic hip joint.
The shoulder of the collar along with the angled transition region from the elongated stem to the platform present difficult manufacturing issues. While the stem is easily susceptible to formation through traditional milling operations, the angled shoulder and transition do not. The manufacturing issues can be complicated by a porous coating that is typically applied to the bone contacting surfaces of the femoral prosthesis.
At present, the femoral prosthesis is rough formed in a casting process. The entire prosthesis body can be surface ground using a known rotary grinding machine. The stem, neck and collar can be blended and polished using known techniques. However, the transition region and the shoulder must be hand blended and polished due to the complicated three-dimensional geometry.
However, the hand polishing process is fraught with inconsistencies. The typical hand polished prosthesis includes peaks and valleys in the surface, and poor blending throughout the transition region and under the shoulder. These inconsistencies can reduce the effectiveness of the fixation of the prosthesis to the femur. There is therefore a need for a manufacturing process that can eliminate these inconsistencies and that can produce a prosthesis that is held to a high tolerance.